The Rangefinder Project
Vanderbilt University
Department of Biomedical Engineering – Senior Design
Project
Date Submitted: December 6, 2012
Alec Coston (BME)
Taylor Coston (BME)
Adil Faqih (BME)
Caleb Huber (BME)
John Lantz (EE)
Abstract ......................................................................................................................................................... 3
Introduction .................................................................................................................................................. 3
History and Context ...................................................................................................................................... 3
Team ............................................................................................................................................................. 4
Work Plan and Outcomes ............................................................................................................................. 5
Evaluation and Sustainability Plan ................................................................................................................ 5
Appendix I: Budget Template with Budget Justification ............................................................................... 7
Appendix II: Resumes .................................................................................................................................... 7
Appendix III: Additional Supporting Documents .......................................................................................... 8
Abstract
Our team aims to develop a rangefinder for the Aculight infrared neural stimulator.
Since the tool is based on energy delivery, there is a small therapeutic distance window over
which the laser is effective at stimulating nerve bundles past the Action Potential threshold.
Moreover, the safety margin for this tool is less than or equal to one order of magnitude. A
great deal of work has been done in this distance-finding endeavor in the military sector in
addition to the academic sphere. In Appendix III, there is a preliminary drawing of our design.
Our goals are to advance the rangefinder science and also develop this device for crossapplication to other therapies. Our internal measure of success will be to ensure continuity of
measurement and allow for adjustment of target distance. We also want to create a feedback
system to alert the user if they are nearing the edges of the range. A third possible goal would
be to integrate distance data to allow for modulation of laser intensity. Some questions remain
about how intensity will fall off over distance and any obstacles that might exist between the
nerve stimulator and the target. Some possible solutions considered were ultrasonic, optical
triangulation, capacitive sensing, confocal chromatic, eddy current sensing and interferometry.
The final modality chosen was ultrasonic distance sensing.
Introduction
Neurosurgical procedures can often require the utmost precision in excising or
manipulating of tissue. Incorrect positioning on the part of the surgeon can lead to unforeseen
and undesired complications. These dangers include damage to neuronal tissue as it can be
difficult to distinguish from the surrounding tissue. The Acculight Infrared Neural Stimulator
has been developed to elucidate the position of the nerve to better allow the surgeon to avoid
coming in unnecessary contact with the nerve bundles. The Acculight Infrared Neural
Stimulator works through a transfer of energy to the nerve. If the laser is too intense the nerve
can be damaged but if it is too weak, the nerve will not be stimulated and cannot be found.
The intensity of the beam is a function of the distance of the laser to the nerve. The basis for
the Rangefinder project is to develop a system to sense the distance between the laser tip and
the nerve. This will allow alterations of beam intensity to maximize nerve stimulation and
minimize damage to the nerve. With the progression of this project, surgeons can better
determine the location of the nerve and how best to avoid it while still adequately performing
the procedure at hand.
History and Context
We began in the divergent thinking stage of design and learned about the problem we
are attempting to tackle and generated possible modalities that could be used as a solution. We
have fostered a relationship with our advisor, Dr. Jansen, and he has given us information on
laser theory and roadblocks to anticipate. We came up with six device categories: optical
triangulation, capacitive sensing, ultrasonic sensing, confocal chromatic, eddy current sensing
and interferometry. We met with our advisor, Dr. Jansen, and a representative from Lockheed
Martin for convergent thinking on December 5th. Taking into account resolution constraints,
physical constraints, and cost we decided that we would pursue ultrasonic proximity sensor
technology for our project. Ultrasonic sensors are commonly used in air and are cheap, small,
accurate, and provide great resolution. The UM18 ultrasonic proximity sensor meets all of our
design specifications. The prototype schematic is shown in appendix III.
Our customers, initially, will be the surgeons employed at Vanderbilt Medical Center.
The device will assist surgeons in operations involving nerve tissue, so it will be primarily (but
not exclusively) used by neurosurgeons. If data from successful trials in Vanderbilt OR’s can be
obtained, the product will be marketed to surgeons and medical centers around the United
States.
Team
Alec Coston, a biomedical engineering major, has experience with various programming
languages, primarily C++ and python. This, combined with John Lantz’ knowledge of integrated circuits
and microcontrollers, will be useful in the design of a digital display and an auditory feedback system.
Taylor Coston has a strong background in biomedical research and helped design a device to
characterize electrical signals from the body. He has a strong background in programming, which may
prove invaluable in writing software for the project.
Adil Faqih is another of the Biomedical Engineering students on the team. Adil brings previous
design and project experience, having worked on surgical probe systems and cardiovascular bioreactors
in other labs. His BME background allows for a biologically focused view of project needs and
requirements.
Caleb Huber brings experience in FDA Quality and compliance with 21 CFR 820 from two
internships in the Quality Division at Roche Diagnostics. He also has experience with project planning
and budgeting from internships at Rolls-Royce North America.
John Lantz is an Electrical Engineer. He specializes in microelectronics and signals and systems.
He is going to be working to integrate the different microelectronics subsystems to make the working
rangefinder. His previous design experiences include a front-end multi-stage feedback amplifier for an
LMR receiver, a parking lot space counter, and vocal recognition software.
Work Plan and Outcomes
This device will further academic knowledge of rangefinder technology. Exploring the
application of rangefinder technology to biological targets in a surgical setting will add useful
information and proof of concept to surgical literature. Even if we do not engineer new
technology, we will create a cheaper probe that can be inexpensively distributed to medical
centers. We hope that our device will be a useful tool for many surgeons across the country,
giving us a large market and few competitors. If our device is successful and easy to use for our
Vanderbilt surgeon collaborator, we will have enough momentum to secure commercial sales in
other medical centers.
We will follow a Design For Six Sigma (DFSS) or DMADV methodology for the design of
this product. This will entail 5 steps as follows: Define, Measure, Analyze, Design, and Verify.
We will also use conventional techniques of schedule and budget tracking over time. At the end
of our project, we will be able to show the budget and schedule variance from our original
baseline and our most recent baseline.
At the end of the grant period, it is our hope that the new device will be used by
physicians in a variety of situations. Selective Dorsal Rhizotomies (SDRs) are performed by
Neurosurgeons frequency and is one of the target applications for this device. Our team will
would also attempt to find other bio-photonic applications for this device. Promoting this
device to neurosurgeons and developing it to suit their needs is a potential future direction for
this product. Any novel features that the Rangefinder might have will be considered for their
patentability.
Figure 1 shows a Gantt Chart outlining the basic steps of our project. Our goal is to
narrow down our long-list of options to a short list and to iterate through the steps of design
for each of these candidates until we find a reliable and cost-effective solution.
Evaluation and Sustainability Plan
Overall we will have succeeded in our project if we create a rangefinder device that can
be integrated into the optical nerve probe and is useful to research and/or surgery. A successful
design will enhance the safety of the patient by regulating either the distance from the probe to
the nerve or the intensity of the laser to ensure proper stimulation without damaging tissues.
There are several levels of success that we have identified:
Level 1: A prototype is created that measures distance from nerve to probe. The precision of
the device must be better than 500 microns and the range must be 2-5 mm.
Level 2: The device is small enough that it can be integrated into an optical nerve probe.
Level 3: The device is safe, efficient, affordable, and appeals to a wide enough market to massproduce.
Level 4: Laser intensity will be modulated by a feedback response from the ultrasonic distance
sensor.
Level 5: Novel aspects of our design project have a positive effect on the proximity sensor
design community.
Making the rangefinder device sustainable is not a difficult task because, as with most
sensors, a long functional life is expected. This is an intrinsic property of proximity sensors;
since the sensor is not in contact with the surface of interest loss of functionality will only occur
over a very long period of time.
Appendix I: Budget Template with Budget Justification
Budget
December
End of
Year
January
February
March
April
$0
$0
$150
$0
$150
$150
$0
$75
$0
$0
$0
$0
$0
$0
$300
$450
$60
$300
$660
$0
$0
$75
$0
$0
$0
$1,185
$0
$0
$0
$0
$0
$0
$10
$0
$10
$30
$0
$30
$30
$150
$180
$220
$0
$0
$0
$0
$0
$0
$0
$450
$300
$150
$450
$1,120
$300
$0
$300
$405
$0
$0
$0
$180
$750
$2,155
Equipment
Laser model
Laser associated parts
(hand-tool)
Wiring
Ultrasound Technology
Total
Other supplies
Printing costs
Poster
Total
Labor
Machining costs
Consultations
Total
Total expenses
Appendix II: Resumes
Appendix III: Additional Supporting Documents
Prototype schematic